A reflective display device in which total internal reflection is twice controllably frustrated at an interface between materials having different refractive indices and in which subtractive color filtration is employed to yield full color images.
U.S. Pat. No. 5,959,777 (the ""777 patent, which is incorporated herein by reference) titled xe2x80x9cPassive High Efficiency Variable Reflectivity Image Display Devicexe2x80x9d and issued Sep. 28, 1999 discloses a multiple pixel image display device. Each pixel has at least one element having a reflective state in which incident light undergoes total internal reflection (xe2x80x9cTIRxe2x80x9d), and having a non-reflective state in which TIR is prevented (i.e. xe2x80x9cfrustratedxe2x80x9d). Such prevention is achieved by modifying the evanescent wave associated with TIR. Specifically, a member is positioned adjacent the element and deformed between first and second positions. In the first position, a gap remains between the member and the element to allow the evanescent wave to have the usual characteristics for TIR. In the second position, the member is in optical contact with the element (that is, the gap thickness is substantially less than an optical wavelength), substantially interfering with the evanescent wave, thus preventing TIR.
U.S. Pat. No. 5,999,307 (the ""307 patent, which is incorporated herein by reference) titled xe2x80x9cMethod and Apparatus for Controllable Frustration of Total Internal Reflectionxe2x80x9d and issued Dec. 7, 1999 discloses controllable switching of a TIR interface by means of an electronically actuated, micro-structured, elastomer member to controllably deform the member into optical contact with the interface, within a continuously variable range of optical contact values, to produce the non-reflective state.
U.S. Pat. No. 6,064,784 (the ""784 patent, which is incorporated herein by reference) titled xe2x80x9cElectrophoretic, Dual Refraction Frustration of Total Internal Reflection in High Efficiency Variable Reflectivity Image Displaysxe2x80x9d and issued May. 16, 2000 discloses that an electrophoretic medium can be used to controllably frustrate TIR in an image display device employing prismatic reflective surfaces. xe2x80x9cElectrophoresisxe2x80x9d is a well known phenomenon whereby a charged species (i.e. particles, ions or molecules) moves through a medium due to the influence of an applied electric field.
U.S. patent application Ser. No. 09/324,103 (the ""103 application, which is incorporated herein by reference) filed Jun. 2, 1999 and titled xe2x80x9cElectrophoretic, High Index and Phase Transition Control of Total Internal Reflection in High Efficiency Variable Reflectivity Image Displaysxe2x80x9d, discloses usage of charged particles suspended in a medium to electrophoretically control TIR at a retro-reflective surface on a high refractive index material; usage of a prismatic structure to redirect ambient light from an overhead light source toward a display image and then from the image to the viewing region in front of the image, yielding a high contrast reflective display; usage of a transparent planar waveguide to frontlight a color display; control of TIR at a retro-reflective surface by means of a vapour-liquid phase transition; and, control of TIR by changing the absorption coefficient of a material using electrical, chemical and/or electrochemical methods.
U.S. patent application Ser. No. 09/449,756 (the ""756 application, which is incorporated herein by reference) filed Nov. 26, 1999 and titled xe2x80x9cOptical Switching by Controllable Frustration of Total Internal Reflectionxe2x80x9d discloses an optical switch for controllably switching a TIR interface between reflective and non-reflective states. In one embodiment, the switch has a stiff-surfaced elastomer dielectric. A separator maintains a gap between the TIR interface and the dielectric""s surface. Variation of a voltage applied between electrodes on the interface and the dielectric""s surface moves the stiffened surface portion into or away from optical contact with the TIR interface. In another embodiment, the optical switch incorporates a cell containing a fluid. One side of the cell forms a light incident interface. A membrane is suspended in the fluid. One pair of electrodes is applied to opposite sides of the membrane; and, another electrode pair is applied to the side of the cell forming the interface and to the cell""s opposite side. A variable voltage potential is applied between selected ones of the electrodes. Application of the voltage potential between selected ones of the membrane and cell electrodes moves the membrane into optical contact with the interface, producing the non-reflective state at the interface. Application of the voltage potential between other selected ones of the membrane and cell electrodes moves the membrane away from optical contact with the interface, producing the reflective state at the interface.
U.S. patent application Ser. No. 09/585,552 (the ""552 application , which is incorporated herein by reference) filed Jun. 2, 2000 and titled xe2x80x9cEnhanced Effective Refractive Index Total Internal Reflection Image Displayxe2x80x9d, discloses an image display with parallel, macroscopically planar, structured surface, non-light absorptive light deflecting and reflecting portions which are longitudinally symmetrical in mutually perpendicular directions, both of which are perpendicular to the preferred viewing direction. A liquid containing a plurality of movable members contacts the light reflecting portion. A controller applies an electromagnetic force to selectively move the members into an evanescent wave region adjacent the light reflecting portion to frustrate TIR of light rays at selected points on the light reflecting portion. The structured surfaces on the light deflecting portion deflect light rays incident in the preferred viewing direction toward the light reflecting portion by imparting to the rays a directional component in the direction of longitudinal symmetry of the light reflecting portion. The structured surfaces on the light reflecting portion totally internally reflect the deflected light rays toward the light deflecting portion at points other than the selected points at which TIR is frustrated. Then, the structured surfaces on the light deflecting portion again deflect the totally internally reflected light rays, cancelling the directional component therefrom, such that the deflected totally internally reflected light rays emerge from the display in a direction substantially parallel to the preferred viewing direction.
The present invention improves upon the prior art by facilitating production of color displays.
The invention provides a color display having a spatially uniform distribution of at least first and second types of prism structure. The first type of prism structure consists of a first prism and a first color filter positioned to filter light incident upon a first facet (i.e. base) of the first prism. The first color filter has a first selected spectral absorption characteristic. A first member having a second selected spectral absorption characteristic is movable with respect to a second facet of the first prism between a first position in which the first member is in optical contact with the second facet, producing a first absorptive state in which total internal reflection of light rays at the second facet is reduced as a function of wavelength in accordance with the second selected spectral absorption characteristic, and a second position in which the first member is not in optical contact with the second facet, producing a first reflective state in which light incident upon the second facet is totally internally reflected toward a third facet of the first prism. A second member having a third selected spectral absorption characteristic is movable with respect to the third facet of the first prism between a third position in which the second member is in optical contact with the third facet, producing a second absorptive state in which total internal reflection of light rays at the third facet is reduced as a function of wavelength in accordance with the third selected spectral absorption characteristic, and a fourth position in which the second member is not in optical contact with the third facet, producing a second reflective state in which light incident upon the third facet is totally internally reflected toward and through the first color filter.
The second type of prism structure consists of a second prism and a second color filter positioned to filter light incident upon a first facet (i.e. base) of the second prism. The second color filter has a fourth selected spectral absorption characteristic. A third member having a fifth selected spectral absorption characteristic is movable with respect to a second facet of the second prism between a fifth position in which the third member is in optical contact with the second facet of the second prism, producing a third absorptive state in which total internal reflection of light rays at the second facet of the second prism is reduced as a function of wavelength in accordance with the fifth selected spectral absorption characteristic, and a sixth position in which the third member is not in optical contact with the second facet of the second prism, producing a third reflective state in which light incident upon the second facet of the second prism is totally internally reflected at the second facet of the second prism.
The spectral absorption characteristics are selected such that, for any selected set comprising proximate ones of all of the types of prism structure included in the display, controlled movement of the members between particular selected combinations of their possible respective positions causes the set to reflect light which has an average spectral reflectance characteristic corresponding to any one of three independent colors, with no one of the independent colors being obtainable by mixing any other two of the independent colors.
Advantageously, the second type of prism structure also has a fourth member having a sixth selected spectral absorption characteristic. The fourth member is movable with respect to a third facet of the second prism between a seventh position in which the fourth member is in optical contact with the third facet of the second prism, producing a fourth absorptive state in which total internal reflection of light rays at the third facet of the second prism is reduced as a function of wave-length in accordance with the sixth selected spectral absorption characteristic, and an eighth position in which the fourth member is not in optical contact with the third facet of the second prism, producing a fourth reflective state in which light incident upon the third facet of the second prism is totally internally reflected toward and through the second color filter.
The spatially uniform distribution preferably includes a third type of prism structure consisting of a third prism and a third color filter positioned to filter light incident upon a first facet (i.e. base) of the third prism. The third color filter has a seventh selected spectral absorption characteristic. A fifth member having an eighth selected spectral absorption characteristic is movable with respect to a second facet of the third prism between a ninth position in which the fifth member is in optical contact with the second facet of the third prism, producing a fifth absorptive state in which total internal reflection of light rays at the second facet of the third prism is reduced as a function of wavelength in accordance with the eighth selected spectral absorption characteristic, and a tenth position in which the fifth member is not in optical contact with the second facet of the third prism, producing a fifth reflective state in which light incident upon the second facet of the third prism is totally internally reflected toward a third facet of the third prism. A sixth member having a ninth selected spectral absorption characteristic, the sixth member movable with respect to a third facet of the third prism between an eleventh position in which the sixth member is in optical contact with the third facet of the third prism, producing a sixth absorptive state in which total internal reflection of light rays at the third facet of the third prism is reduced as a function of wavelength in accordance with the ninth selected spectral absorption characteristic, and a twelfth position in which the sixth member is not in optical contact with the third facet of the third prism, producing a sixth reflective state in which light incident upon the third facet of the third prism is totally internally reflected toward and through the third color filter.